1. Technical Field of the Invention
The present invention generally relates to the field of smelting technology. More particularly, it relates to a method of high efficient dross removal from the surface of liquid iron
2. Background of the Invention
After the pre-treatment of desulfurization, desiliconization and dephosphorization, the liquid iron will produce a great amount of solid slag which floats on its surface. The solid slag must be removed away promptly. Otherwise it may impair the pretreatment effect of the liquid iron, leading to the rise in production cost of the next processes.
The existing slagging-off device (scooping-up device) in the process of pretreatment of liquid iron has been used since the 1950's or 1960's. This kind of slagging-off machine for liquid iron is of linear reciprocating type, driven mechanically or hydraulically. A slag rake, which is made of refractory material, is mounted on a cantilever of the machine. By immersing the rake into the liquid iron to a certain depth and making it moving along the surface of liquid iron in linear or curved reciprocating manner, it can rake out the solid slag floating on the surface of liquid iron in the ladle gradually.
However, the conventional slagging-off technique and the equipment have disadvantages as follows:
(1) Long time taking for the work of slagging-off, and low working efficiency. Normally, it would need to reciprocate for over ten or even tens of times, which takes 5 to 10 minutes;
(2) Incomplete de-slagging and low de-lagging rate. By adding a slag adhesive agent or a slagging-off agent so as to conglomerate the slag, the de-slagging rate can just reach 80% to its maximum. The incomplete de-slagging would directly bring about much more resulfurization in converter or electric furnace;
(3) Liable to carry away liquid iron while raking out slag, generally with an iron loss between 0.5% and 1.0%. These problems have already become a worldwide problem that troubles the international iron and steel industry and constrains the development in this field. The direct economic loss incurred thereof is over 0.5 billion US dollars each year.
Over the recent years, rapid development has been seen in China's iron and steel industry, with an overall yield reaching the first place in the world. It was estimated that a pretreatment amount of liquid iron could reach 50 million tons in 2003. But, as the technology and equipment are relatively backward, the actual iron loss rate is mostly around 1.0%. Together with the economic loss caused by resulfurization in converters and electric furnaces, the direct economic loss a year would be over 0.5 billion RMB.